Effect of PH on Amylase RPA

Question 1

What colour does iodine turn if starch is present

Answer 1

Blue/ black

Question 2

What colour is iodine solution

Answer 2

Orange

Question 3

Why do we leave all the test tubes in the water bath for 10 mins before mixing them together

Answer 3

Allow them to reach the correct temperature (use a thermometer to check)
So that the rate of enzyme activity isn’t affected by temperature

Question 4

How can we tell that the reaction is complete (all starch has broken down into glucose)

Answer 4

Iodine solution no longer turns black so starch isn’t present (as it has all been broken down into glucose)

Question 5

Method

Answer 5

1) place one drop of iodine solution into each well of a spotting tile
2) Take 3 tests tubes- for one add 2cm cubed buffer solution, for one add 2cm cubed amylase solution, for one add 2 cm cubed starch solution
3) Leave all test tubes in water bath for 10 mins at 25 degrees so that the solutions reach the correct temperature
4) Mix all the test tubes together, place back in the water bath an immediately start the time
5) use a stirring rod to add one drop of iodine onto the first well
6) repeat every 30s until the iodine solution no longer turns black and record the time taken for this to happen (all the starch has been broken down so the reaction is complete)
7) Repeat steps 1 to 6 using buffer solutions with a different PH
8) Calculate rate of enzyme activity for each buffer solution by doing 1/ time taken for solution to stay orange and not turn black and compare results for each PH

Question 6

How to calculate rate of enzyme activity with time taken

Answer 6

1/ time taken for solution to stay orange and not turn black

Question 7

1 safety precaution

Answer 7

Wear safety goggles as iodine solution is an irritant

Question 8

Does a shorter time taken for the solution to stay orange mean a faster or slower rate of reaction

Answer 8

Faster
As all of the starch has been broken down into glucose more quickly
(Therefore at this PH it is closest to the optimum temperature for amylase to work at)

Question 9

Sources of error

Answer 9

Intervals between testing may be too long to accurately find the time taken for the starch to be completely broken down
Colour change open to interpretation as its gradual (e.g some of the solution might be black but not all)- so get multiple people to observe the well to decide if the reaction is complete
PH value is to resolution of 1 so not very accurate

Question 10

How could we overcome the time taken not being very accurate as we are using 30 second intervals

Answer 10

Test the solution every 10 seconds instead